Wikipedia:Reference desk/Archives/Science/2014 May 11

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May 11

Rings and moons

A simple definition of a moon is any body that orbits a planet, can be seen from Earth and has been named. However the number is greatly increased if one chooses to call "moon" small bodies such as Dactyl, only 1.4 km diameter, in orbit round asteroid 243 Ida. Dactyl was serendipitously detected by Galileo and has not been seen either from Earth or by the Hubble Space Telescope. 84.209.89.214 (talk) 18:39, 11 May 2014 (UTC)

Since planetary rings consist of small rocks and recently discovered moons don't have large diameters, I'm wondering when is the chunk of rock considered a moon? I don't know the exact definitions, but isn't then every piece from a ring theoretically a moon? --2.246.58.160 (talk) 16:12, 11 May 2014 (UTC)

A moon would need to be separate and distinct. The rings of Saturn, for example, look like solid objects, although we know they're not. The Voyagers and other exploratory vehicles didn't see individual particles of the rings (as far as I know) even from relatively close range. Saturn's moons, in contrast, are large enough to be visible on their own. ←Baseball Bugs ^{What's up, Doc?} carrots→ 16:18, 11 May 2014 (UTC)

According to the section §The definition of a moon in our article Natural satellite, the definition is vague, but the implication is that objects that are "too small" are not normally labelled as moons. —Quondum 16:23, 11 May 2014 (UTC)

The implication is "large enough to be seen". The article indicates that the individual particles of the rings have not been directly observed. ←Baseball Bugs ^{What's up, Doc?} carrots→ 16:28, 11 May 2014 (UTC)

I don't see where you get that. It leads to a nonsensical dependence on factors such as where the observation is being made from relative to the body under consideration, resolving power of the optical system being used, ambient lighting (e.g. distance from the Sun), and albedo. Do you have a reference? While there may be roots in what could be observed by specific people at a certain point in history, to use such an interpretation without more context in modern times is worse than vague. —Quondum 19:22, 11 May 2014 (UTC)

Feel free to give us your interpretation of what the article says. ←Baseball Bugs ^{What's up, Doc?} carrots→ 20:29, 11 May 2014 (UTC)

The section that I linked to, when discussing a lower limit, says "Every natural celestial body with an identified orbit around a planet of the Solar System, some as small as a kilometer across, has been identified as a moon, though objects a tenth that size within Saturn's rings, which have not been directly observed, have been called moonlets." This would suggest a criterion of size might be considered since no other criterion is mentioned, but what is clearest is the lack a formal definition of what a "moon" or "natural satellite" is defined to be in this sense. The clause "which ..." does not relate to a definition as stated, as it simply adds information. —Quondum 22:31, 11 May 2014 (UTC)

This question is purely a matter of definition. What do we mean when we use the word "moon" ? Who has authority to define that word? We could pull out a reputable dictionary, like the Oxford English Dictionary or Wiktionary: wikt:moon. The OED cites four hundred years of English usage in which "moon" refers to an object other than Earth's primary natural satellite ...including this barely-passable snippet in which moon appears to refer to an extrasolar planet. I would nitpick the definition, but many language-scholars attest that John Milton's writings define the English language we speak today).

Alternately, we could defer to an astronomy subject matter expert, or to an authoritative organization, like NASA or the International Astronomical Union, or the American Geophysical Union; or even, lest we stray into fringe territory, we might even ask the Planetary Society. Were we to publish a peer-reviewed paper, we could defer to the editorial board of our journal for a definition; if we violated that definition without good cause, we probably couldn't get published. But, alas. there is not a lot of active debate on the definition of "moon", because new discoveries of moon-like entities are somewhat rare. The recent kerfuffle about the definition of "planet" - culminating in the formal IAU definition of planet - was important, because we have new technology that is allowing us to discover new extrasolar planets. Scientists needed to formalize and standardize their terminology so that they could efficiently communicate new knowledge at the cutting edge of our observational capabilities. Reputable organizations, like IAU and NASA weighed in on the issue.

But moons are not presently an area of active research. If you go back just a few decades - say, to 1954 - you'd find voluminous writings by reputable scientific authorities about moon terminology. Is lunar sand "dust" or "dirt"? Neither! It's regolith. And when we study the interior of the moon, are we conducting geology or geophysics? Neither! It's selenology. Can a terrain feature be called a deep valley or canyon, even if it wasn't eroded? No, those are rills, and moons have rilles. And a flat plain-like area ... that would be a mare. The point in an orbit that makes its closest approach to a moon a perigee? No, it's a perilune. And so on. An entire specialized vocabulary was created, because lots of educated people were talking about moon things.

Today, lunar research is nearly dead. The Lunar Science Institute aggregates legacy research publications, but doesn't sponsor new scientific inquiry. You'd be hard-pressed to find a "moon expert" on the payroll of any physics or astronomy department at most universities. The IAU does not publicize definitions for lunar terminology these days. So, we ought to defer on the definition to whatever the dictionary says; that definition will be vague and suitable for general purpose" usage. For the details, we can point you to articles in Wikipedia or elsewhere that summarize everything we know about moons - Earth's moon and elsewhere among the cosmos. I can recommend several great books:

• Planetary Sciences, (de Pater & Lissauer), co-authored by one of the NASA scientists who defined the Kepler mission to search for extrasolar planets. This text has an entire chapter on moons and moon formation, and is up-to-date with everything that we have learned about moons from 21st century space-travel and science.
• Strange World of the Moon: an excellent book written before the Apollo missions. This book presents an incredibly robust theoretical overview of the moon and its geology selenology. It also provides great context for the non-Earth-moon enthusiast, because you can read for yourself how accurately we were able to remotely ascertain lunar properties before we visited our Moon; and compare to our present-day descriptions of moons around other planets.

Between those two, you'll probably get as robust and formal a definition of "moon" as any scientist can provide.

But it's unlikely that we can find any recent formalized defintion from IAU or anywhere else that explicitly lays out what a "moon" is, in the general sense.

Nimur (talk) 02:12, 12 May 2014 (UTC)

Thanks, that is about as thorough a treatment of the topic as one could ask for. For a simple, accessible web page on the topic, I thought I'd add this: What is a moon?. —Quondum 03:17, 12 May 2014 (UTC)

This one is most definitely not a moon. - ¡Ouch! (^{hurt me} / _{more pain}) 07:29, 13 May 2014 (UTC)

<samll>One of the more consistent criteria is that man-made/artificial objects do not qualify. I wonder what'll happen with natural objects with man-made trajectories. —Quondum 13:33, 13 May 2014 (UTC)

"samll"? LLO.

Same here. The criteria of "destroying the Earth" are satisfied if the planetary mass is redistributed into two spherical bodies. By that definition, Earth has been "destroyed" more than once. First, the collision with Theia (planet), and if you count this as the moment of its creation, you still have the launch of Sputnik and man after that. The only catch is that the spherical bodies aren't even remotely similar in mass.

If only natural bodies can be moons, that's OK so far. Then, it is probably OK to call objects moons only if they are unique in a sense like the small moons within Saturn's rings (there are at least 4 or 5 bodies that stand out, the smallest is about a mile in diameter) but not the millions of pebbles that actually are the rings.

However, this is still a bit arbitrary; in what one counts as "unique." - ¡Ouch! (^{hurt me} / _{more pain}) 14:46, 13 May 2014 (UTC)

And to further complicate matters the Earth is sometimes orbited by minimoons Richerman (talk) 07:40, 12 May 2014 (UTC)

The correct meaning of a Kepleren orbit is an elliptical path to which the orbiting body is bound by the gravitational force of the central attractor; it is periodic and reversible in space-time. The transient interactions of asteroids with Earth's gravity are examples of gravitational slingshot events. I disagree with calling such minimoon one-off trajectories "orbits". 84.209.89.214 (talk) 12:26, 12 May 2014 (UTC)

See also other moons of Earth, quasi-satellite. Wnt (talk) 20:56, 12 May 2014 (UTC)

Moons are still being discovered and the edges of the meaning still debated. See the new moon Peggy, for instance.[1] 75.41.109.190 (talk) 14:46, 12 May 2014 (UTC)

Dove Offspring?

My doves just had babies and according to a calculator, both babies will be orange mutation But neither of them have the color,

The mother is Orange Pearled, The father is a Wild Blond

The calculator displays the father as dwBdwB

The calculator also displays the mother as TaTa dwB- Mm+

Please assist me if you can :>

FYI: The calculator can be found Here

--208.107.179.233 (talk) 19:55, 11 May 2014 (UTC)

Do the feathers of mature doves have the same color as when they first hatch out? ←Baseball Bugs ^{What's up, Doc?} carrots→ 20:30, 11 May 2014 (UTC)

I don't understand the notation of the calculator, but if orange is the dominant trait, the percentage being orange is high. It doesn't automatically result in orange because both parents could have hidden traits you couldn't have considered in your calculation unless you had detailed information about the DNA. --2.246.58.160 (talk) 21:41, 11 May 2014 (UTC)

@Baseball bugs No. Its all down before they shed it and start growing pin feathers — Preceding unsigned comment added by 208.107.179.233 (talk) 23:34, 11 May 2014 (UTC)

I thought so. But are the downy feathers fairly close to the color the feathers will be for an adult, or is there no correlation? ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:26, 12 May 2014 (UTC)

@Baseball No. It barely resembles the adult plumage, if any. — Preceding unsigned comment added by 208.107.179.233 (talk) 03:24, 12 May 2014 (UTC)

Wouldn't that explain why they don't have the color (yet), then? Evan ^{(talk|contribs)} 03:47, 12 May 2014 (UTC)

I agree - I would bet that the color would emerge only as the adult plumage comes in. In many species of animal, the juveniles need really good camoflage to avoid the attention of predators - which changes into more showy colors in adulthood...I wouldn't be at all surprised if the same effect was at work here. SteveBaker (talk) 14:45, 12 May 2014 (UTC)

For those of you who don't know, Here's what a squab/baby dove looks like --208.107.179.233 (talk) 21:05, 12 May 2014 (UTC)